Electrical phase shifters



May 14, 1963 H. scHARFMAN 3,090,015

ELECTRICAL PHASE SHIFTERS Filed March 27, 1957 United States Patent 3,090,615 ELECTRHCAL PHASE SHIFTERS Howard Scharfrnan, Lexington, Mass., assigner to Raytheon Company, a corporation of Delaware Filed Mar. Z7, 1957, Ser. No. 648,897 1 Claim. (Cl. S33-24.1)

This invention relates to electrical phase shifters, and more particularly to adjustable phase-shifting devices utilizing ferrites for electrically controlling the phase of energy traveling from a microwave source in an electromagnetic wave transmission system.

Electrical phase Shifters or ferrite circulators utilizing the Faraday rotation effect have been constructed which consist of a solid ferrite rod axially positioned within a conductive pipe or other waveguide structures. By means of such devices, a plane or linearly polarized electromagnetic wave at microwave frequencies can be rotated when propagated through the ferromagnetic material which is magnetized in a direction parallel to the direction of propagation of the wave by a unidirectional magnetic field-producing means whose field strength is below that at which saturation or ferromagnetic resonance in the ferrite occurs. In such phase-shifting devices, the phase angle between the output electric vector of the electromagnetic wave and the input electromagnetic wave may be varied by rotating the plane of polarization of the electrical energy passing through the ferrite element positioned within the waveguide structure, the angular rotation of the electric vector of the electromagnetic wave depending upon the relative strength of the applied magnetic field. In this manner, the resultant p-hase shift can be used to perform typical impedancematching operations such as, for example, controlling the effective transmission line length between a mismatch and a source of microwave energy.

However, in applications in which a ferrite rotator or circulator .of this type is used to introduce a desired phase shift in a typical circular or square waveguide, the propagated wave, upon emergence from the ferrite rotator, is polarized at a different angle from the original wave and requires that the output flange or section of rectangular waveguide to which the phase-shifting device is connected be angularly rotated and oriented with respect to the input section of waveguide an amount equal to the angular rotation of the electric vector produced by the ferrite rotator. In numerous applications, therefore, it would be desirable to introduce an appreciable predetermined controllable value of phase shift to the electromagnetic wave energy traveling along a microyWave transmission path without introducing a corresponding resultant polarization rotation of the electric vector of the propagated wave due to the Faraday rotation effect.

In accordance with the invention, an electrical phaseshifting device for electromagnetic wave energy, which is independent of the total Faraday rotation and in which the total rotation `of the plane of polarization through said phase shifter will be zero, can be achieved by providing a ferrite element mounted in a circular guide or along the longitudinal axis in a square guide and having a pair of energized coils surrounding the waveguide in the region of the ferrite element and connecting the coils in series opposition. In this manner, two opposing longitudinal magnetic fields produced by the oppositely-connected field coils will provide that the total rotation of the plane of polarization through the two rotators will be zero, independent of the current through the coils. However, the phase shift through the two rotators will be twice that for each rotator and will increase with the applied field through an approximately linear region until saturation of the ferrite elements is reached. Thus, the

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phase of the microwave energy passing through the phaseshifting device can be controlled by Varying the voltage applied to the oppositely-connected field co11s to obtain linear reciprocal phase shift proportional to the applied magnetic field. I

In addition, static phase shift is achieved by applymg a direct current biasing field to the oppositely-connected magnetic field coils suflicient to reach the center of the aforementioned approximately linear region of magnet1c field strength prior to saturation of the ferrite element. By shifting the D.C. biasing current, as noted, the device can be operated to produce a microwave phase shift about the center region in either a positive or negative direction that is approximately linear with field coil current. Also, a combination of `dynamic and static phase shift can be achieved by application of an A.C. current in addition to the direct current in the opposing coils to obtain a mixture of amplitude and frequency modulation in a manner to be described subsequently. By adjusting the static phase shift, the effective line length between a mismatch and the microwave source supplying microwave energy can be controlled.

Other objects and advantages of this invention will be more readily perceived upon analysis of the drawing, in which:

FIG. 1 is an isometric view, partly in section, `of the first embodiment of a phase shifter according to the invention;

FIG. 2 is a graph showing phase shift and rotation for each rotational element as functions of the strength of the applied magnetic field;

FIG. 3 is an isometric view, partly in section, of a further embodiment of the invention wherein separate ferrite elements are provided;

FIG. 4 is a further embodiment of the invention as applied to a circular lwaveguide having a -degree bend; and

FIG. 5 is a circuit diagram showing one way in which both static and dynamic phase shift may be obtained from a ferrite rotator.

Referring to FIG. l, a ferrite circulator or phase shifter is indicated generally by reference numeral 10 and includes a circular waveguide section 12, a cylindrical ferrite element 14 positioned within the waveguide section 12 by means of a low-loss dielectric material 16, such as Teflon, which acts as a solid supporting medium for the ferrite element 14. The Teflon dielectric material may be cut to `the inner diameter of the circular -waveguide section 16, divided into two sections, as shown at 17, in the region of the ferrite element, a hole bottomdrilled in each section, and the ferrite element slidably inserted into the Teflon. Numerous methods for mounting the ferrite within the Teflon will suggest themselves kto those skilled in the art. For example, when the Teflon is to be inserted into a curved section of waveguide, the Teflon may be heated until soft and forced into the curved portion of the waveguide. At each end of the Teflon dielectric 16 and integral therewith are Teflon matching buttons 18 and 19 adapted to provide a standard matching connection from each end of the circular waveguide section 12 to a rectangular, square or circular waveguide member, and which may be secured thereto by means of flanges 21 and 27, as shown in FIG. 2, one or more of which may be rotatable, or in any other suitable manner known to the prior art. A microwave generator (not shown), such as a magnetron or Vklystron oscillator, can be used as a source of microwave energy. The energy can be injected into the waveguide connected to Teflon matching button 18 through an output line, not shown, which may be part of the magnetron. Any type of microwave generator and any standard type matching means for transferring energy 3 from a square, circular or rectangular waveguide into the ferrite rotator may be used, such as a circular matching button, a quarter-wave transformer, irises, and the like, provided that the proper polarization and mode of energy is thereby obtained. In the present instance, an additional length of rectangular waveguide may be connected to Teflon matching button 19 and then to a suitable load or radiating device. The waveguide, so connected, should have a transverse dimension large enough to support the desired transverse electric mode So as to propagate the energy.

In accordance with the invention, the ferrite device 10 further includes two separate magnetic field-producing means such as field coils 22 and 24, oppositely disposed, and surrounding the circular waveguide 12 in the region of the ferrite element 14. The two field coils of 25,000 lturns each are connected in series opposition by means of a connecting lead 25 and are energized by a unidirectional current source 26 of approximately l0 milliamperes by way of leads 28 and 29. Under the iniiuence of the opposing axial magnetic fields, the ferrite phase Shifter 10 has the property of rotating the plane of polarization of microwaves transmitted through one section in a direction which is dependent upon the direction of the applied axial magnetic field; that is, a reversal of the direction of the magnetic field results in reversal of the direction of rotation of the propagated electromagnetic wave through the one section. More particularly, therefore, both the rotation of the plane of polarization and the transmission phase shift through each ferrite rotator section are functions of left and right and circular polarized phase constants, described in detail in an article by M. G. Sakiotis and H. N. Chait, entitled Ferrites at Microwaves in the Proceedings of the IRE, vol. 4l, pp. 87-93, January 1953, and in an article by Howard Scharfman, entitled Three New Ferrite Phase Shifters in the Proceedings of the IRE, vol. 44, pp. l456-1459, October 1956. These phase constants are in turn functions of the applied longitudinal magnetic field. The rotation 0 and the phase shift p can be expressed in terms ofthe phase constants by the following equations:

where is equal to the phase constant of the circularly polarized wave rotating in the same sense as current causing the magnetic field;

is equal to the phase constant of the circul arly polarized wave rotating in the opposite sense of +g and L is equal to the length of the ferrite rod.

The variation of the phase constants as functions of the applied magnetic field for a typical X-band microwave rotator is shown in FIG. 2. Plotted in the same figure are the calculated rotation and phase shift curves. Whereas:

as the magnetic field is increased, the phase shift increases slowly and then passes through the aforementioned approximately linear region and finally saturates the ferrite element. The linear region, therefore, can be used to obtain linear, reciprocal phase shift proportional to the magnetic field. With appropriate D.C. biasing current applied to the ferrite phase shifter shown in FIG. 1, a microwave phase shift, either positive or negative, can be produced which is approximately linear with coil current. In addition, the insertion-loss of the device is independent 0f applied coil currents. For example, a variable standing wave ratio of less than 1.1 is obtained when the ferrite circulator then is connected to l-inch by .5-inch input and output wave guides.

in addition, from examination of the curves shown in FIG. 2, it should be understood that the maximum variation of phase shift of the rotator phase shifter is a function of ferrite length, diameter and saturation magnetization. Therefore, an arbitrarily large electrically variable phase shift can be obtained by increasing the length of the device, providing that symmetry in the two rotator sections is observed. In the latter instance, the rotations and rates of change of rotation of the plane of polarization in the individual rotator sections become substantially large for small changes in applied coil current. However, phase variation up to i degrees can be obtained for use with applications requiring small linear phase variations with low constant insertion loss.

lt should be understood that the ferrite phase shifter 10 can be constructed so as to have two planes of symmetry. It is possible, of course, to utilize a ferrite element of square outer configuration in conjunction with a circular waveguide, or vice versa. It should be further understood that the length of the ferrite element 14 exceeds that of its diameter so that the required magnetic field for a given angle of rotation is held relatively low. It is also desirable to maintain the diameter of the ferrite rod less than one-third the diameter of the waveguide 12 for low-loss attenuation of the propagated wave. As noted, a square or circular waveguide structure which is rotationally symmetrical, and in which the circularly polarized waves have the same phase constant at zero field strength, can be used as the propagation medium. For example, the waveguide section may be of circular, circular-ridged, square or square-ridged types and may be cornpletely filled or partially filled with dielectric, or empty. In the present instance, a rotation of approximately 60 degrees, as shown in FIG. 2, would produce a phase shift of approximately 20 degrees per section.

Referring now to FIG. 3, modification of the singleferrite device of FIG. l is shown, wherein a second ferrite rod or element 15 is mounted or held in position concentrically within the field coil 24, while the ferrite element 14 is held in position within the oppositely-disposed iield coil 22. The operation of this ferrite phase shifter is similar to that of the phase shifter shown in FIG. 1. By appropriately adjusting the static phase of the ferrite phase shifter, the line length between a mismatch and the magnetron or other microwave source may be controlled by changing the effective length of the line to pull the magnetron or microwave source in a known manner as the voltage to the oppositely-disposed coils is varied.

Referring to FIG. 4, the ferrite phase shifter shown in FIG. l may be constructed using a single field coil 23 surrounding ferrite elements 14 and 15 which are oppositely-disposed in a circular waveguide section 30 having a bend at 32. In this embodiment, microwave energy entering the input section containing the ferrite element 14 is rotated a predetermined angular distance. Since the rotation of the plane of polarization will change sense if the direction of the applied field is reversed with respect to the direction of propagation, the propagated wave upon being reversed in direction by the 180 bend, shown .at 32, will enter the output half of the ferrite circulator 33 and undergo an additional phase rotation to restore the wave to the original polarization. However, the accompanying phase shift again will be twice that for each rotator `and will depend upon the applied coil current.

Referring now to FIG. 5, a circuit diagram is shown which provides a means for obtaining both static and dynamic phase shift from a ferrite rotator. As shown, an alternating current source 35 of approximately 100 volts is fed by way of one microfarad blocking condenser 36 to one output terminal 37, and the other side of the source or generator 35 is connected directly to the oppositely disposed output terminal 38 to provide an alternating current at the frequency at which it is desirable to modulate a microwave source. The direct current field is produced by means of a direct current source 39 connected in a series with a one-henry choke 40, which prevents the alternating current from generator 35 from being applied across the direct current source 39. The capacitor 36 prevents the direct current source 39 from being applied across the alternating current source 35. In this manner, direct current, and alternating `current fields may be applied simultaneously to the field coils of the ferrite circulator to produce a static and dynamic phase shift in order to frequency or amplitude modulate a microwave source. For example, a magnetron may be frequency or amplitude modulated by varying the phase of a mismatch seen by the magnetron by inserting the phase shifter between the mismatch and the magnetron. By adjusting the static phase of the phase-shifting element, the line length between the mismatch and the magnetron can be controlled. Application of an alternating current field to the phase-shifting element will produce a dynamic phase change of the mismatch as seen by the magnetron. A combination of frequency modulation and amplitude modulation may be produced in a known manner, depending upon the operating point of the magnetron and upon the length of the path between the magnetron and the load, as varied by the alternating current and direct current fields applied to the ferrite circulator.

It should be understood that other methods of modulation may be obtained by means of the ferrite circulator. For example, phase modulation of a glystron, magnetron, or other microwave device, is also possible depending upon the wave shape of the current through the field coils of the ferrite circulator. In one type of phase modulation, a sawtooth current can be applied to the circulator field coils to produce a single sideband output displaced in frequency from the input frequency by a. controlled amount. In addition, the electrical phase shifter can he used to control the microwave phase energy in a waveguide system either in open loops or closed feedback loops, or in antenna scanning systems to modify radiation beams and patterns as well as the individual gain of an antenna system. A biasing current or permanent magnet producing a longitudinal field may be applied to one coil in excess of that to the other coil to produce a net rotation. In this instance, the device acts as a phase shifter as aforementioned, and in addition, a desired controllable rotation is achieved. Also, two permanent magnets of equal strength and opposite plurality may be used in place of the field coils to produce a fixed phase shift with zero rotation, or permanent magnets of unequal strength may be used to produce a desired rotation and phase shift.

For the foregoing reasons, it is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. Moreover, the invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in 'the art. iIt ris, accordingly, desired lthat the appended claim be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

A device for producing an electrical phase shift of a polarized electromagnetic wave comprising a waveguide receptive of said electromagnetic wave, ferrite element means positioned within said waveguide, the outer periphery of said ferrite element means being similar in configuration to that of said waveguide, means including a pair of energized coils connected in series opposition surrounding said waveguide in Ithe region of said ferrite element means, means for supplying a direct current bias to said coils, and means for impressing an alternating current on said direct current bias, thereby providing a static and dynamic phase shift in said electromagnetic wave for any value of current flowing through said coils and independently of amplitude modulation and polarization rotation of said electromagnetic wave.

References Cited in the file of this patent UNITED STATES PATENTS 2,748,353 Hogan May 29, 1956 2,773,245 Goldstein et al. Dec. 4, 1956 2,787,765 Fox Apr. 2, 1957 2,802,184 FOXv Aug. 6, 1957 2,806,972 Sensiper Sept. 17, 1957 2,830,289 Zaleski Apr. 8, 1958 2,857,574 Anderson Oct. 21, 1958 2,907,964 Schafer Oct. 6, 1959 OTHER REFERENCES Modern Advances in Microwave Techniques, published July 1955, pages 76-78. 

